A track assembly is a vehicle propulsion system in which a continuous belt (also known as a band, a tread, or a track) is driven by one or more drive wheels. Track assemblies are widely used in military equipment (e.g., tanks), construction equipment (e.g., bulldozers), and farm equipment (e.g., tractors). Military equipment and heavy construction equipment typically have belts made of interconnected metal plates. Farm equipment typically have belts made of reinforced synthetic rubber. When compared to wheels, a track assembly makes contact with the ground over a much greater surface area. The increased surface area provides greater traction, less compaction of the ground, and improved ability to function in muddy conditions.
A wide variety of track assemblies are known. A simplified track assembly 10 is shown in FIGS. 1 to 4. The track assembly has a drive wheel 20, an unpowered idler wheel 30, a road wheel 40 (also known as a bogie wheel), and a belt 50. The wheels are typically formed of an inner wheel 21 and an outer wheel 22 with a recessed inner portion 23. The double wheel construction reduces weight. The inner surface of the track contains a series of guide blocks 51 that fit within the inner wheels and the outer wheels and keep the track aligned. The track is shown in phantom lines in FIG. 2 for illustration purposes. A section of the track is shown in FIG. 3 with the height of the guide blocks exaggerated for illustration purposes. The track assembly is shown from an end in FIG. 4. The upper and lower portions of the track are shown as sections. The upper and lower portions of the track are shown spaced apart from the double wheels for illustration purposes.
Track assemblies on farm equipment (agricultural implements) work well in the fields where the weight of the vehicle is distributed over the entire ground-contacting portion of the track. However, farm equipment must often be driven on paved roads. When driven on paved roads, the weight of the vehicle is concentrated where the double wheels contact the lower portion of the belt. For example, a track assembly having a contact surface area in a field of twenty or more square feet may have an effective contact surface area on a paved road of only one or two square feet. The small effective contact surface area causes heating and rapid wear on the rubber belt.
The rubber belts on farm equipment sometimes contain transverse teeth on their inner surfaces for engaging drive wheels having gears. Such belts are disclosed in Smith, U.S. Pat. No. 2,476,460, Jul. 19, 1949; and Price, U.S. Pat. No. 5,018,591, May 28, 1991. These transverse teeth do not support the drive wheels. In other words, the drive wheels do not exert a downward gravitational force upon the transverse teeth.
The rubber belts on farm equipment sometimes contain guide blocks running lengthwise along the belt for keeping the belt in alignment. Such belts are disclosed in Purcell et al., U.S. Pat. No. 5,433,515, Jul. 18, 1995; Keehner, U.S. Pat. No. 6,086,169, Jul. 11, 2000; and Gingras, U.S. Pat. No. 7,252,347, Aug. 7, 2007. These guide blocks do not support the drive wheels. In other words, the drive wheels do not exert a downward gravitational force upon the guide blocks.
Although a variety of track assemblies are known, there continues to be a demand for an improved track assembly. More particularly, there is a demand for a track assembly with an increased effective contact area between the wheels and the belt when the vehicle with the track assembly travels on a paved road.